Surge protectors are required in many areas of electrical engineering. The problem arises time and time again that the surge protectors need to be reliable while not being excessively expensive to manufacture.
Typically, surge protectors have an overvoltage protection device and a disconnector. One example of an overvoltage protection device is a varistor.
The thermal disconnector protects the overvoltage protection device and disconnects it from the network in the event of an overload or advanced aging of the overvoltage protection device.
For this purpose, an opening is usually provided in the housing (inner housing) through which the tab of the overvoltage protection device is electrically contacted.
This wall separates the overvoltage protection device into two logical regions. One side contains the overvoltage protection device and the other side the arc interrupt, for example.
Plasma can form when the overvoltage protection device is rapidly overloaded, which produces a high temperature and high pressure. By virtue of the opening in the wall, however, plasma is able to flow from one side of the wall to the other.
This effect is usually promoted by the fact that the wall is damaged/deformed by the thermal effect of plasma/arc.
However, this impairment/damage can also result in the functioning of the disconnecting device being impaired or damaged. For example, guide rails and slide surfaces of the disconnecting means can be deformed.
This can lead to substantial problems, since the overvoltage protection device can now be seriously damaged, which can cause explosions and/or fires.
In order to address these problems, a wide variety of solutions have been proposed in the past; for example, the guide rails and slide surfaces of the disconnecting means have been appropriately reinforced and/or spring forces for disconnection and hence the force on the disconnector substantially over-dimensioned in order to compensate for the effect of the plasma on the disconnection devices (friction, counterforce by the plasma).
The extinguishing capacity of today's disconnecting devices is limited by mechanical loading (destruction of the overvoltage protection device). If cutoff occurs at excessively high currents, the damage can result in a non-functional disconnecting device.